In recent years, for the purpose of digitalizing image information and transmitting and accumulating information at high efficiency at that time, devices complying with a scheme such as a Moving Picture Experts Group phase (MPEG) in which compression is performed by orthogonal transform such as discrete cosine transform (DCT) and motion compensation using specific redundancy of image information have been spread for both information delivery of broadcasting stations or the like and information reception in general households.
Particularly, an MPEG 2 (ISO/IEC 13818-2) scheme is defined as a general-purpose image coding scheme, and now being widely used for a wide range of applications of professional use and consumer use as a standard covering an interlaced scanned image, a progressive scanned image, a standard resolution image, and a high-definition image. Using the MPEG 2 scheme, for example, a high compression rate and an excellent image quality can be implemented by allocating a coding amount (a bit rate) of 4 to 8 Mbps in the case of an interlaced scanned image of a standard resolution having 720×480 pixels and a coding amount of 18 to 22 MBps in the case of an interlaced scanned image of a high resolution having 1920×1088 pixels.
The MPEG 2 mainly aims for high-quality coding suitable for broadcasting, but does not support a coding scheme of a coding amount (bit rate) lower than that of MPEG 1, that is, a coding scheme of a high compression rate. As mobile terminals are spread, a need for such a coding scheme has been considered to increase in the near future, and an MPEG 4 coding scheme has been standardized. ISO/IEC 14496-2 has been approved on December, 1998 as an international standard for the MPEG 4 image coding scheme.
Further, in recent years, standardization of a standard such as H.26L (ITU-T Q6/16 VCEG) designed for image coding for video conferencing at first has been conducted. H.26L is known to require a more computation amount for encoding and decoding than in a coding scheme such as MPEG 2 or MPEG 4 but be able to implement high coding efficiency.
Further, in recent years, as one of MPEG 4 activities, standardization of incorporating a function that is not supported by H.26L based on H.26L and implementing high coding efficiency has been conducted as Joint Model of Enhanced-Compression Video Coding. This standardization has been approved on March, 2003 as an international standard in the name of H.264 or MPEG-4 Part10 (Advanced Video Coding (AVC)).
Furthermore, as an extension thereof, Fidelity Range Extension (FRExt) including an encoding tool necessary for professional use such as RGB or YUV422 or YUV444 or 8×8 DCT and a quantization matrix which are specified in MPEG-2 has been standardized on February, 2005. As a result, the AVC scheme has become a coding scheme capable of also expressing a film noise included in a movie well and is being used in a wide range of applications such as a BD (Blu-ray (a registered trademark) Disc).
However, in recent years, there is an increasing need for high compression rate coding capable of compressing an image of about 4000×2000 pixels which are 4 times as high as a high-definition image or delivering a high-definition image in a limited transmission capacity environment such as the Internet. To this end, an improvement in coding efficiency has been under continuous review by Video Coding Expert Group (VCEG) under ITU-T.
Currently, in order to further improve coding efficiency to be higher than in the AVC, standardization of a coding scheme called High Efficiency Video Coding (HEVC) has been being conducted by Joint Collaboration Team-Video Coding (JCTVC) which is a joint standardization organization of ITU-T and ISO/IEC. Non Patent Document 1 has been issued as a draft as of August, 2012.
Meanwhile, the image coding schemes such as the MPEG-2 and the AVC have a scalable function of hierarchizing and encoding an image. According to the scalable function, it is possible to transmit encoded data according to a processing performance of a decoding side without performing a transcoding process.
Specifically, for example, it is possible to transmit only an encoded stream of an image of a base layer that is a layer serving as a base to terminals having a low processing performance such as mobile phones. Meanwhile, it is possible to transmit an encoded stream of an image of the base layer and an image of an enhancement layer that is a layer other than the base layer to terminals having a high processing performance such as television receivers or personal computers.
The HEVC scheme also has the scalable function, and in the HEVC scheme, a video parameter set (VPS) including parameters related to the scalable function is defined in addition to a sequence parameter set (SPS) and a picture parameter set (PPS) as described in Non Patent Document 1.
FIG. 1 is a diagram illustrating an exemplary syntax of the VPS in the HEVC version 1.
In an HEVC version 1, since only a scalable function (hereinafter, referred to as a “temporal scalability”) of hierarchizing and encoding an image according to a frame rate is provided, only parameters related to the temporal scalability are defined in the VPS as illustrated in FIG. 1.
In an HEVC version 2, standardization of supporting a scalable function other than the temporal scalability as well is scheduled to be conducted.